The present invention relates to a heater cable for immersion in a liquid to be heated in a container for any desired purpose. More particularly, it is adapted for immersion in a solution in a container to maintain the solution at a desired temperature during a plating operation.
In the design and manufacture of electrical resistance heaters for immersion in liquid baths, or immersion heaters, as they are called, it is desirable to protect the electrical heating element from any corrosive effects of the bath. It is also desirable to have a high degree of flexibility to the heater cable to permit coiling or winding on supports to increase the length of heater which may be immersed in the bath. Flexible immersion heaters having an inert plastic encasing the heating element are known in the art, as for example, those described in U.S. Pat. Nos. 3,674,985 and 3,657,520 issued to M. A. Ragault. However, such known immersion heaters lack the desired flexibility because a solid linear heating element is used with a braided glass sheath covered with a coating of rubber bonded to the outer surface of the sheath. A heater cable has been disposed in a coiled arrangement in the liquid to be heated as in the Ragault U.S. Pat. No. 3,674,985 patent; however, the prior art heater cable has employed a solid linear conductor. Such an arrangement has been found limited in its flexibility, and therefore unable to provide the desired heating capacity for a cable occupying a given amount of space in the solution.